The present invention relates to gas turbine combustors and more specifically to the end cover that directs the fuel to the fuel injectors of a combustor.
A gas turbine engine typically comprises a compressor, at least one combustor, and a turbine. The pressure of air passing through the compressor is raised through each stage of the compressor and is then directed towards the combustion system. Gas turbine combustion systems typically comprise multiple components to properly and efficiently mix fuel with the compressed air in order to ignite this mixture to create hot combustion gases. The hot combustion gases are then directed towards a turbine, which produces work, typically for thrust, or shaft power if the engine shaft is connected to an electrical generator.
A typical combustion system includes a combustion liner where ignition occurs of the fuel and air mixture. Due to the operating pressures of the combustion system, the combustion liner is usually contained within a case or pressure vessel. Fixed to this case is an end cover that typically directs the flow of fuel from a fuel source to the fuel injectors for injection into the combustion liner. Depending on the type of performance and emissions desired from the combustor, the combustion system can burn both liquid and gaseous fuels. As a result, the end cover must be capable of handling different fuel types, large temperature gradients and pressure forces, such that no mixing of fuel types occurs within the end cover.
Temperatures of the end cover can range typically range between 250 and 700 degrees F. with pressures upwards of 250 lb/in2.
A known method of providing a combustor end cover meeting the goal of delivering multiple fuel types separately involves utilizing braze joints within the end cover.
A prior art example of this type of end cover configuration is disclosed in U.S. Pat. No. 6,112,971, which discloses an improved vacuum brazing process to avoid joint failures. In a typical brazing process, two components that are to be joined together are first machined having very tight tolerances. For example, referring to FIGS. 1A and 1B, insert 12, which is brazed to end cover 14, has a diametrical gap 13 between insert 12 and end cover 14 of 0.001-0.005 inches. Braze paste or foil, which is of an acceptable material for bonding the two components, is then taped or injected by syringe into gap 13. The end cover is then placed in a furnace and heated and cooled according to a predetermined cycle, such that the insert bonds to the end cover to produce a joint capable of handling the temperature gradients and pressures applied to the end cover.
While brazing can provide the desired joint between mating components, the process does have its drawbacks, especially with respect to its application on a combustion end cover. Depending on the configuration, often times the resulting joint cannot be inspected visually, which is the preferred inspection technique. As a result, more costly and time-consuming inspection procedures are required, such as pressure testing, x-ray, and ultrasonic inspection. Furthermore, the brazing process requires, as previously specified, tight tolerance gaps between components to be joined together, which are more costly to manufacture. What is needed is a simpler more cost effective end cover configuration that can flow multiple fluids separately without requiring the brazing processes well known in the prior art.